When scientist Junko Nakanishi stepped into radiation-contaminated towns and villages in Fukushima Prefecture 10 months after the nuclear power plant meltdowns of 2011, she realized how difficult the job of decontamination would be.

Surveying the thinly populated areas surrounded by hills and rice paddies, she wondered how much time and money it would take to reduce the radiation.

“I thought decontamination wouldn’t succeed without a concrete plan,” Nakanishi, 76, a leading expert on chemical risk assessment, said in a recent interview with The Japan Times.
[…]
An annual dose of 1 millisievert has meanwhile been set as a “long-term goal” for decontamination, without a specific time frame.

Nakanishi said that the 20 millisievert threshold is too high for many residents to accept and that the 1 millisievert figure is unrealistic in heavily contaminated areas, given the limits and cost of decontamination technology. As an alternative, she proposes a maximum exposure level of 5 millisieverts per year as a target for decontaminating evacuation zones, based on her assessment of the various risk factors.

“Somebody has to find a common ground where people can return to their homes as early as possible. We need to set a goal for radiation. . . . But no politician, bureaucrat or expert seems to make such suggestions,” she said. As a scientist, Nakanishi said it’s her job to find that magic number.
[…]
Nakanishi looked at health factors, technological limits, cost and time to assess the tainted areas in Fukushima and concluded that an annual radiation exposure of 5 millisieverts or less would be the best goal for repopulating them.

According to her calculations, a 5-millisievert goal would allow some 65,000 residents to return home in another one to two years and cost around ¥1.8 trillion to execute.
[…]
Nakanishi also emphasized that there is a need for the government to financially back those who want to relocate even if an annual radiation dose drops to less than 5 millisieverts a year. Given Japan’s experience with the atomic bombings of Hiroshima and Nagasaki, some find it extremely hard to prevent horrific images of the aftermath from entering their minds when they hear the word radiation, she said.

One Response

Junko Nakanishi has had a distinguished career beginning with her courageous criticism of water quality back in the 1970s. Her latest engagement in the “science” of risk assessment raises serious issues for all of us to consider, but this particular chapter–on coming up with a “magic number” (albeit the reporting newspaper’s language) –on permissible, rational decontamination/radiation exposure goals for evacuees to return to their homes in Fukushima highlights some of them. To begin with, there seems to be a presumption that the desirable goal is for evacuees to return. Shouldn’t the pros and cons of that presumption be subjected to rigorous debate? Secondly, whose interests are prioritized in the calculations of risk? To her credit, Nakanishi states that the government should support those “who want to relocate” anyway, but realistically, once a level such as 5 millisieverts is endorsed by scientists, why would that happen? Risk assessment is a limited but probably necessary tool, but (a) appropriate procedures are hardly self-evident and (b) the implications of the findings far exceed the realm of science and are properly subjects of philosophical and moral debate.

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